AERODROME FORECASTS

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AERODROME FORECASTS

• PART A
• TREND FORECASTS

FOURTH EDITION August 2005
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TREND FORECASTS

• TREND forecasts are appended to a METAR or SPECI.

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TREND FORECASTS

• TREND forecasts are appended to a METAR or SPECI.
• The information contained in the TREND is a
  forecast covering period of two hours from the
  time of observation.

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TREND FORECASTS

• TREND forecasts are appended to a METAR or SPECI.
• The information contained in the TREND is a
  forecast covering period of two hours from the
  time of observation.
• The TREND forecast indicates significant changes
  in respect of one or more of the elements
  surface wind, prevailing visibility, weather and
  cloud.

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TREND FORECASTS

• Example
• METAR OJAM 170900Z 29012KT 5000 HZ SKC NOSIG

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TREND FORECASTS

• Example
• METAR OJAM 170900Z 29012KT 5000 HZ SKC NOSIG
• METAR OJAM 170900Z 29012KT 5000 HZ SKC BECMG
  FM0930 TL1030 22025KT 3000 BR BKN030

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TREND FORECASTS

• METAR OJAM 170900Z 29012KT 5000 HZ SKC BECMG
  FM0930 TL1030 22025KT 3000 BR BKN030

• CHANGE INDICATORS (BECMG or TEMPO)
• The change indicator BECMG is used to describe
  expected changes in the meteorological
  conditions.
• The change indicator TEMPO is used to describe
  forecast temporary fluctuations in the
  meteorological conditions.

The indicator PROB shall not be used in TREND
forecasts
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TREND FORECASTS

• METAR OJAM 170900Z 29012KT 5000 HZ SKC BECMG
  FM0930 TL1030 22025KT 3000 BR BKN030

The time group GGgg Preceded without a space by
one of the letter indicators FM (from), TL
(until), AT (at)
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TREND FORECASTS

• METAR OJAM 170900Z 29012KT 5000 HZ SKC
• BECMG FM0930 22025KT 3000 BR BKN030
• BECMG TL1030 22025KT 3000 BR BKN030
• BECMG FM0930 TL1030 22025KT 3000 BR BKN030
• BECMG AT1000 22025KT 3000 BR BKN030

• Note
• When changes are forecast to take place at
  midnight UTC, the time is indicated as follows
• By 0000 when associated with FM and AT
• By 2400 when associated with TL

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TREND FORECASTS

• METAR OJAM 170900Z 29012KT 5000 HZ SKC BECMG
  FM0930 TL1030 22025KT 3000 BR BKN030

• SURFACE WIND
• TREND indicates changes in the surface wind which
  involve either
• A change in the mean wind direction of 60
  degrees or more, (with speed 10 kt or more).
• A change in the mean wind speed 10 kt or more.

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TREND FORECASTS

• METAR OJAM 170900Z 29012KT 5000 HZ SKC BECMG
  FM0930 TL1030 22025KT 3000 BR BKN030

VISIBILITY Improving or reduction
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TREND FORECASTS

• METAR OJAM 170900Z 29012KT 5000 HZ SKC BECMG
  FM0930 TL1030 22025KT 3000 BR BKN030

• WEATHER PHENOMENA
• Any weather phenomena which are expected to cause
  a significant change in visibility.
• To indicate the end of the occurrence of
  significant weather phenomena, the abbreviation
  NSW (Nil Significant Weather) replaces this
  group.

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TREND FORECASTS

• METAR OJAM 170900Z 29012KT 5000 HZ SKC BECMG
  FM0930 TL1030 22025KT 3000 BR BKN030

• CLOUD or VERTICAL VISIBILITY
• Significant changes in cloud are indicated when
  one or more of the following conditions are
  expected
• The height of the base of a cloud layer of BKN or
  OVC extent is below or expected to fall below
  1500 ft.
• The cloud amount is forecast to change from
• SCT, FEW or SKC, increasing to BKN or OVC
• BKN or OVC decreasing to SCT, FEW or SKC
• The sky is expected to remain or become obscured,
  vertical visibility observations are available,
  and the forecast indicates changes in vertical
  visibility.

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TREND FORECASTS
THE END